A189828 Numbers k for which d(k-1) + d(k+1) is a record, where d(k) is the number of divisors of k.

2, 3, 5, 7, 11, 17, 19, 29, 41, 71, 161, 169, 181, 239, 419, 701, 721, 881, 1079, 1681, 2159, 2519, 2521, 4031, 4159, 5039, 7561, 8399, 10081, 13441, 13859, 18721, 20161, 22679, 25199, 27719, 27721, 35281, 45361, 50399, 50401, 55439, 65519, 110879, 138599

Offset

1,1

Comments

Many of these terms are in A090481, which restricts k to be prime. The record values are in A189829.

Links

Donovan Johnson, Table of n, a(n) for n = 1..135

Mathematica

DeleteDuplicates[Table[{n, DivisorSigma[0, n-1]+DivisorSigma[0, n+1]}, {n, 2, 140000}], GreaterEqual[#1[[2]], #2[[2]]]&][[;; , 1]] (* Harvey P. Dale, Jul 14 2025 *)

Crossrefs

Cf. A090481, A189827, A189829.

Sequence in context: A228424 A347192 A335325 * A090481 A094342 A164641

Adjacent sequences: A189825 A189826 A189827 * A189829 A189830 A189831

Keyword

nonn

Author

T. D. Noe, Apr 28 2011

Status

approved